AgWeatherNet Weekly Weather Outlook for August 9 to August 15, 2021

Another strong heat wave expected this week

Mark Ingalls, AgWeatherNet Intern

Synopsis:

A dome of high pressure is forecast to build over the Western United States this week resulting in another strong heat wave. This is not expected to be as significant as the June event, but highs in the 90s to near 100 are likely for many Western Washington lowlands with the hottest days falling on Thursday and Friday. East of the Cascades, the hottest locations may approach 110 with the hottest days Friday and Saturday. Limited winds should create hazy conditions from wildfire smoke. Toward the weekend, a few monsoonal thunderstorms are possible in the eastern mountains. Sunday, an upper level trough dropping southeast from Alaska should bring some cooling, but the degree to which temperatures lower remains uncertain.

Discussion:

The upper level low responsible for almost fall-like conditions over the previous weekend is on its way out. A ridge of high pressure is building across the Western United States and Canada in its place, which is forecast to produce warming temperatures in Washington this week. West of the Cascades, highs will rise from the 70s and low 80s on Monday to the mid 80s to the low 100s on Thursday and Friday, which will be the warmest days. Offshore flow will extend these hot temperatures all the way to the coast on Thursday, but the wind pattern reverses Friday to offer some relief within a few miles of the ocean for Friday.

In Eastern Washington, the hottest days are forecast to be Friday and Saturday when most lowland locations will be over 100. The lowest elevations, such as the Columbia Basin, Gorge, and Yakima Valley may approach 110 these days. An area of low pressure off the Northern California coast during this period may pull enough monsoon moisture into the region to generate some afternoon thunderstorms in and near the Blue Mountains, but right now this chance remains low. Throughout the lowlands on both sides of the Cascades, overnight lows are likely to be in the mid 60s to upper 70s.

Saturday, an upper level trough dips southeastward out of Alaska to turn the flow pattern to out of the northwest and moderate temperatures in Western Washington somewhat, spreading into Eastern Washington on Sunday. There is a bit of uncertainty to how effective this cooling will be. Recent runs of the GFS are all in on this, offering highs in the mid 60s for the Puget Sound Region and near 90 for the Columbia Basin on Sunday. The European model is significantly more reserved with highs on Sunday in the 80s to near 90 around Seattle and Tacoma and still near 105 around the Tri-Cities and Moses Lake.

A look at the ensembles helps to narrow things down. Using Pasco on Sunday as an example, the GFS ensembles offer high temperatures ranging from 79 to 110. The European ensembles are far less varied but lie on the hot end, leading to greater confidence in that solution. Slow cooling is likely to continue into the beginning of next week, but temperatures should remain above average for mid-August.

Generally light winds at the surface and aloft are likely to bring a return to hazy conditions through the week. In areas where the smoke becomes dense, temperatures may not reach as high as forecast. This will probably only be a difference of a few degrees, but is notable nonetheless.


8 to 14 Day Outlook, August 16 to August 22, 2021
  • Above average temperatures and below average precipitation are favored for the period.

Important Points About This Week's Weather

South Central Washington
Remainder of the Week
  • Wind: Generally light and W/SW through Wed, N Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 90s Tue, low 100s Wed-Thu, mid 100s Fri.
  • Low Temps: Upper 50s Mon night, mid 60s Tue night, low 70s Wed-Fri nights.
  • Sky Cover: Mostly clear, hazy.
Weekend
  • Wind: W with breezy areas.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 100s Sat, low 100s Sun.
  • Low Temps: Low 70s Sat & Sun nights.
  • Sky Cover: Mostly clear, hazy.

North Central Washington
Remainder of the Week
  • Wind: Generally light and W/SW through Wed, N Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 90s Tue, low 100s Wed, mid 100s Thu-Fri. Cooler in higher terrain.
  • Low Temps: Mid 60s Mon night, low 70s Tue night, mid 70s Wed-Thu nights, upper 70s Fri night. Cooler in higher terrain.
  • Sky Cover: Mostly clear, hazy.
Weekend
  • Wind: W with breezy areas.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 100s Sat, near 100 Sun. Cooler in higher terrain.
  • Low Temps: Mid 70s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly clear, hazy.

Eastern Washington
Remainder of the Week
  • Wind: Generally and W/SW through Wed, N Thu-Fri with breezy areas.
  • Precipitation: Low chance of thunderstorms S of Pullman Fri.
  • High Temps: Near 90 Tue, mid 90s Wed, upper 90s Thu, low 100s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Upper 50s Mon night, low 60s Tue night, mid 60s Wed-Fri nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly clear, hazy.
Weekend
  • Wind: W with breezy areas.
  • Precipitation: Low chance of thunderstorms S of Pullman Sat.
  • High Temps: Low 100s Sat, upper 90s Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Upper 60s Sat night, mid 60s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly clear, hazy.

Western Washington
Remainder of the Week
  • Wind: Generally light. N through Thu, W Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Tue, mid 80s Wed, mid 90s Thu-Fri. Cooler in higher terrain and along the coast.
  • Low Temps: Upper 50s Mon night, mid 60s Tue-Wed nights, upper 60s Thu-Fri nights. Cooler in higher terrain.
  • Sky Cover: Mostly clear, hazy areas.
Weekend
  • Wind: Generally W, breezy areas Sun.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 90s Sat, mid 80s Sun. Cooler in higher terrain and along the coast.
  • Low Temps: Mid 60s Sat night, low 60s Sun night. Cooler in higher terrain.
  • Sky Cover: Mostly clear, hazy areas.

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Washington State University